Why can't you stick your smartwatch on the glass of a high-speed train? Because you might not be able to take it off...

Produced by: Science Popularization China

Author: Denovo

Producer: China Science Expo

A new "light bulb incident" is hot! Recently, the Internet has set off a wave of "don't stick smart watches on high-speed rail glass". This sentence has become the latest "don't swallow light bulbs" warning. However, many netizens just don't believe it and have to try it themselves. As a result, after sticking the Apple watch on the high-speed rail glass, they found that it was firmly attached and could not be removed... They even tore the watch screen apart to remove the watch. This scene seems to have seen the classic scenes of "licking iron bars in winter" and "swallowing light bulbs" again!

There are more than 100,000 related notes

(Image source: Screenshot by the author)

There are already more than 100,000 related notes on social platforms. So what exactly causes the Apple Watch to stick to the high-speed rail glass and cannot be removed?

"Glossy glue phenomenon"? Not really

Some people attribute this to the "optical bonding phenomenon", which can also be called optical contact bonding - that is, when the surfaces of two objects are extremely smooth, the distance between molecules is reduced and the intermolecular force is strong, causing the two to fit closely.

Speaking of the "optical interference phenomenon", we have to mention the optical interference phenomenon first studied by Newton in 1666. At that time, Newton placed a convex lens on a flat glass and observed a series of concentric light and dark ring stripes around the contact point. These stripes are caused by the interference of light waves caused by the thin air layer formed between the lens and the glass.

Newton's Rings

(Image source: Wikipedia)

In optical research, if two optical surfaces are not sufficiently flat and in close contact, a thin air layer may cause interference and produce fringes similar to Newton's rings.

It was not until 1900 that optical contact bonding began to be used in the construction of optical prisms. Over the next century, this phenomenon was further studied.

However, photobonding usually occurs under laboratory conditions and requires extremely high surface flatness and cleanliness . Conformal accuracy refers to the degree of matching of the surface shape and structure of two objects, that is, whether they can fit tightly when in contact. If the conformal accuracy of the objects is less than 1 nanometer, there will be enough surface area in close contact for the molecular interaction to produce an observable macroscopic effect - that is, the two objects stick together.

However, the screen material of the Apple Watch, such as Ion-X glass or sapphire glass, although finely processed, its surface smoothness is not enough to cause the glossy phenomenon. Similarly, the window glass of high-speed rail is highly polished, but its surface roughness is not enough to cause this phenomenon.

The author also looked at his own weathered watch, which had countless scratches on the surface. It should not be able to stick to the high-speed rail glass.

The author's weathered smartwatch

(Photo credit: Photo taken by the author)

It’s not magic, it’s the “membrane” method

After many attempts, some netizens found that even if the watch surface and the high-speed train window glass were wiped very clean, the watch still could not be firmly attached to the glass window. In this regard, some people speculated that this may be related to whether the watch screen is covered with a protective film, especially the material properties of the hydrogel film.

The hydrogel film is softer and can better fit smooth surfaces. When the hydrogel film of a watch is attached to a smooth surface such as glass, the air in the middle can be expelled during the bonding process, and its flexible material can form a closed small cavity between the smooth surface, thereby forming negative pressure. This phenomenon is similar to the working principle of the bathroom suction cup in our daily life - the generation of negative pressure allows objects to be tightly attached to the smooth surface and can withstand heavy hanging objects.

The author bought a hydrogel film. Since he couldn't wear the watch on the high-speed train to enjoy the scenery during the journey, he created the conditions at home to let the watch enjoy the night view outside the window. The watch was successfully attached to the glass!

Put the watch with hydrogel film on the glass

(Photo credit: Photo taken by the author)

How to remove the watch stuck on the glass?

When the watch is firmly attached to the high-speed rail glass, pulling it hard will not only be useless, but may also damage the watch screen. Therefore, the correct way to remove it is to destroy the adsorption force of this negative pressure . The following methods can be tried:

First, you can use air to enter the adsorption area to break the negative pressure. Take a thin plastic card (such as an ID card or transportation card) and carefully insert it into the gap between the watch and the glass. Slowly move the card while gently lifting one side of the watch to allow air to gradually enter the fitting area. When air enters, the negative pressure effect will weaken and the watch will naturally fall off.

The use of lubricant is also an effective method . Apply a small amount of water or hand sanitizer to the gap to destroy the fit through the lubricant. It is recommended to use a cotton swab to dip the liquid to prevent excess liquid from flowing into the watch. As the adsorption force weakens, gently shake the watch to remove it.

You can also try to rotate the watch or use the temperature difference to remove the watch , hold the edge of the watch and gently rotate it to break the tight fit of the adsorption. No matter which method you take, avoid using too much force to avoid damaging the watch or the glass surface.

Knowing the dangers, there are still so many people "swallowing light bulbs"

Although we know that certain behaviors may bring dangers, we still choose to try them, such as "sticking the watch to the high-speed rail glass", "licking the iron rod in winter", "swallowing light bulbs" and other risky behaviors. There are many reasons behind this psychological phenomenon.

First of all, curiosity is a natural driving force of human beings. When faced with taboos or warned behaviors, people's curiosity will be further stimulated, and they want to explore the real consequences behind this "forbidden fruit". There is a " forbidden fruit effect " in psychology, which means that when something is clearly prohibited, its appeal will increase. In addition, luck is also an important reason that drives people to try risky behaviors. They may think, "Accidents only happen to others, and I can avoid risks by being careful."

Swallowing light bulb

(Image source: generated by the author’s AI)

Another important factor is the mentality of conformity and challenge . In social media and online communication, some high-risk behaviors are packaged as symbols of "challenge" or "testing the limits", which are easy to attract people to imitate, especially young people who are more inclined to seek recognition through such behaviors. At the same time, some people will choose to try dangerous behaviors because of their rebellious mentality against authority or rules, in order to show their personality and independence.

The combination of these psychological factors, coupled with the underestimation of the consequences of risks, leads some people to try high-risk behaviors without hesitation even in the face of clear warnings.

Conclusion

The phenomenon of Apple Watch being adsorbed on the glass of high-speed railway has once again triggered public discussion on dangerous behaviors driven by curiosity. This phenomenon not only involves the discussion of physical principles, but also reveals the "forbidden fruit effect", fluke mentality and herd behavior in human psychology. Although this attempt seems to be just fun on the surface, it may cost a high price behind it, such as damaging expensive equipment or even endangering your own safety. Readers should still try it with caution!

References:

[1] Rayleigh, Lord. "Optical contact." Nature 139.3523 (1937): 781-783.

[2] Haisma, Jan, and GACM Spierings. "Contact bonding, including direct-bonding in a historical and recent context of materials science and technology, physics and chemistry: historical review in a broader scope and comparative outlook." Materials Science and Engineering: R: Reports 37.1-2 (2002): 1-60.

[3] Alexe, Marin, and Ulrich Gösele, eds. Wafer bonding: applications and technology. Vol. 75. Springer Science & Business Media, 2013.

[4] Myatt, Chris, Nick Traggis, and Kathy Li Dessau. "Optical Contacting: Changing the Interface of Optics."